In a wireless system with reuse of frequency resource, ICI introduced by the frequency reuse is an important factor limiting the downlink capacity. When an mobile terminal located in the cell boundary, that is, inter-cell area, receives a significant signal from its dominating base station (Base station, BS), it also receives signal from other base station(s) via the same time-frequency resource. And the signal from other base station(s) constitutes an interference to this mobile terminal.
In an OFDM/OFDMA system, there are 2 solutions involving cooperation among multiple base stations to solve the foregoing issue, as bellows:
1. Macro Diversity
Based on the solution of Macro macro diversity, for a mobile terminal located in the cell boundary, both the base station (BS) to which the mobile terminal currently belongs and the base station (BS) to which the mobile terminal are approaching send the same signal via the same time-frequency resource, i.e. time slot and sub-carrier. Thus, interference suppression and diversity gain can be achieved since the base stations have individual transmission channels respectively.
The drawback of macro diversity solution lies in that adjacent base stations are required to send the same signal to the same mobile terminal via the same time-frequency resource, which limits the total user number supported by the system.
2. Network MIMO
Base on network MIMO, all antennas of all base stations act together as a single radio antenna array. According to all the Channel Status Information (CSI), e.g. channel response array, between all base stations and mobile terminals, a precoding matrix is generated to enable the joint precoding among multiple base stations to eliminate the co-channel interference (CCI) among user terminals. Since the CSI between all base stations and mobile terminals are taken into account in the precoding of this technology, interference introduced by reuse of time-frequency resource is diminished to the extreme extent by network MIMO and optimal performance is attained.
The optimal performance is attained, yet at the expense of introducing an extremely high computation complexity, by the above solution, and it is of a more severity that since each base station needs an exchange of its own related channel information via the backhaul network, wherein the backhaul network is used for the interaction of the data and signaling between base stations and between base station(s) and its(their) scheduling apparatus, a high consumption of network resource caused by large scale of information transmission improves the backhaul network load and delay of the information transmission degrades system performance.
Thus, a new solution is needed to overcome the above issue in the current technology, which should suppress the above interference effectively without introducing too much requirement for the consumption of backhaul network resources, and meanwhile have a low computation complexity.